At least 20 people were killed in a crowd crush at an aid distribution site run by the Gaza Humanitarian Foundation (GHF), the controversial Israeli- and US-backed organization said Wednesday, the first time it has acknowledged deaths at one of its sites.

According to the GHF, the people died in a “chaotic and dangerous surge,” which it said was “driven by agitators in the crowd.” The aid group said 19 people were trampled and one person was stabbed in the crowd crush.

The GHF alleged that individuals who were “armed and affiliated with Hamas” deliberately instigated the chaos. “For the first time since operations began, GHF personnel identified multiple firearms in the crowd, one of which was confiscated,” it said.

Hamas’ Government Media Office (GMO) blamed the GHF for the incident, claiming the group called on Palestinians to receive aid at the site in Khan Younis, southern Gaza, then “proceeded to lock the iron gates after herding thousands of starving people into narrow iron corridors.”

The Palestinian health ministry said 21 people were killed in the incident, 15 of whom died from suffocation after tear gas was fired at a crowd of people awaiting aid, triggering a crowd crush. The other six people were shot in the upper body by Israeli forces, it said.